DESCRIPTION: (Applicant's Abstract) One of the principal actions of cannabinoids is to inhibit the secretion of the important reproductive hormones luteinizing hormone (LH) and prolactin (PRL) from the anterior pituitary via a hypothalamic site of action. The overall goal of this proposal is to understand the cellular mechanism(s) by which cannabinoids affect the excitability of neurons in the medial preoptic area (POA) and the arcuate nucleus (ARC) of the hypothalamus to decrease the secretion of LH and PRL. C annabinoid effects will be studied in the guinea pig because in the female the reproductive cycle and gonadal steroid hormone profile parallel those of the female primate. For comparison, studies also will be conducted in males to examine potential sex differences. Females are ovariectomized one week prior to, and treated with estradiol benzoate 24 hr prior to, experimentation to control for inherent variations in gonadal steroid hormones. Intact males are injected with sesame oil vehicle 24 hr before experimentation to control for injection effects. Specifically, I will determine the distribution of the G-protein coupled brain cannabinoid (CB1) receptor in the POA and the mediobasal hypothalamus in Specific Aim 1 using radioligand and GTP gamma S autoradiography. In Specific Aim 2, I will evaluate whether cannabinoids indirectly excite A12 dopamine neurons. This will be accomplished using sharp electrode and whole-cell patch clamp recordings with biocytin-filled electrodes in hypothalamic slices. I will ascertain whether cannabinoids inhibit GABAergic ARC interneurons known to inhibit A12 dopamine neurons by modulating K+ currents and/or synaptic input; thereby attenuating GABAA receptor-mediated synaptic input onto this latter group of neurons and ultimately affecting a disinhibition. In Specific Aim 3, I will determine if cannabinoids inhibit gonadotropin-releasing hormone neurons in the POA and ARC by modulating K+ conductances and/or synaptic input using sharp electrode and whole-cell patch clamp recordings with biocytin-filled electrodes in hypothalamic slices. These studies will integrate electrophysiological, pharmacological and molecular biological techniques into a multidisciplinary approach to study cannabinoid actions in hypothalamic neurosecretory cells, and will help to elucidate the cellular mechanism(s) underlying cannabinoid-induced suppression of critically important reproductive hormones.